This invention relates to a vehicle engine ignition timing system of the type utilizing adaptive knock retard in which memory cells store slowly changed values based on sensed knock which are used to retard ignition timing. Such cells are preferably non-volatile so as to retain the values between periods of engine operation; and the values are thus available upon each re-initiation of engine operation.
Engine knock, however, is temperature dependent. There is a much greater tendency for an engine to knock at high engine temperatures than at low engine temperatures. When an engine becomes completely warmed up after some period of operation, its temperature is controlled to a substantially predetermined temperature, under normal conditions, by the coolant flow regulating action of a thermostatic valve. This temperature is typically much higher than the ambient temperature outside the vehicle engine compartment. During engine operation, the memory cells of the ignition timing system may be slowly adjusted toward greater retard by the increased knock at the higher temperature.
However, after the engine has ceased operation for some time and cooled to the ambient temperature present outside the vehicle engine compartment, it has much less tendency to knock; and significantly less timing retard is desired. This is particularly the case where the vehicle has remained non-operated overnight and is started in the cooler ambient temperatures of the morning. In such cases, easier starts and smoother cool running may be obtained with less retard. However, the memory cells will take some time to gradually advance the timing; and, in fact, the engine control may be programmed to make no changes to the cells until the engine is fully warmed up and operating in a stable engine operating mode. This can leave the ignition timing less than optimally advanced during cold start and warmup.